The actress, who plays Michelle Connor in ‘Coronation Street’, has been reliving her loss as she filmed a stillbirth storyline for the soap earlier this year.
Speaking about what got her through, Marsh told The Mirror: “My family were unbelievably supportive.
“I would walk through the door and Polly would be there running round and asking what is for dinner. She doesn’t care whether I have had a bad day or not, she just wants her mum.”
Marsh called Polly her “little miracle”, adding: “She is a little whirlwind. From the second she opens her eyes in the morning, she is just energy. She loves life, and to see her I think ‘Thank God for you’.
“We all feel like that about Polly. I think it is because we lost Archie and we didn’t think we were going to have Polly.”
Marsh said she wanted to do the storyline for ‘Coronation Street’ - where her character had a stillbirth at 23 weeks - to raise awareness and educate people about baby loss and late miscarriage.
She said talking about her loss also helped with her healing.
Previously blogging about the topic on HuffPost UK, Marsh said it upsets her that her son Archie does not have a birth certificate, despite giving birth to him.
“While Archie was only on this earth for a few short minutes, he existed to me,” she wrote. “He was, and will always be, my little boy and there’s not a day goes by that I don’t think of him.
“You see, according to UK law as it stands, a parent cannot be issued with a birth certificate if the child is born showing no signs of life before 24 weeks.
“In my case, Archie arrived at 21 weeks back in 2009 - before the 24 week cut-off period - and therefore we never received a birth certificate.
“To go through such a thing, and then to not even have him acknowledged in an official capacity, was heartbreaking for me.”
Marsh is also mum to Emilie, 19, and David, 21, from a previous relationship.